The present application claims priority from Japanese Application No. 2003-002633, filed on Jan. 8, 2003.
The present invention relates to a process for preparing vinylpyrrolidone polymer powder, which has high bulk density and favorable powder flowability and can be handled with ease.
Conventionally, when drying an aqueous solution of a vinylpyrrolidone polymer, a spray dryer (see JP-A-8-208741) or a drum dryer has been used. However, the vinyl pyrolidone polymer powder obtained by using these methods under the conditions of the prior art has low bulk density and poor powder flowability. Therefore, conventional vinylpyrrolidone polymer powder is difficult to handle. Also, because the weight per unit volume is small, there is the problem that costs for exporting become high, regardless of transportation by air or sea. Particularly, the above problem is noticeable in the case of a vinylpyrrolidone polymer with a low K value.
The present invention aims to provide a process for preparing vinylpyrrolidone polymer powder, which has high bulk density and favorable powder flowability and can be handled with ease.
The present invention relates to a process for preparing vinylpyrrolidone polymer powder, which comprises spraying an aqueous solution of a vinylpyrrolidone polymer into a drying tower using a disc atomizer and then drying; wherein the peripheral speed of the disc of the disc atomizer is at least 4,500 m/minute, the temperature of hot air introduced into the drying tower (temperature of heat entering tower) is 165xc2x0 to 300xc2x0 C. and the temperature discharged from the drying tower (temperature of heat escaping tower) is 100xc2x0 to 140xc2x0 C.
The aqueous solution of a vinylpyrrolidone polymer is preferably sprayed from a disc atomizer installed on the upper part of the drying tower into the drying tower and dried while falling.
A drying tower with a height of at least 9 m and a diameter of at least 5 m is preferably used.
The speed of water evaporation (L/minute)/peripheral speed of disc (m/minute) in the drying tower is preferably 0.0001 to 0.009 (L/m).
The K value (value representing molecular weight according to the Fikentscher method) of the vinylpyrrolidone polymer is preferably 10 to 60.
The bulk density of the vinylpyrrolidone polymer powder is preferably at least 0.50.
According to the present invention, vinylpyrrolidone polymer powder, which has high bulk density and favorable powder flowability and can be handled with ease, can be prepared.